Manufacture of organolead compounds



United States Patent MANUFACTURE OF ORGANOLEAD COR/[POUNDS Sidney M. Blitzer and Tillmon H. Pearson, Baton Rouge, La., assignors to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application March 28, 1955 Serial No; 497,373

6 Claims. (Cl. 260-437) stantially to NaPb, with ethyl chloride according to the following equation 47 4NaPb+4C H Cl= (C,H Pb +3Pb+4NaCl With the highest yields obtained thereby, only about 22 percent of the lead present in the NaPb alloy is converted to tetraethyllead. Under conditions of best operation of this process, no one heretofore, as far as we are aware, has been able to increase this yield of tetraethyllead by even a' few percent, due to the inherent limitation in yield as is apparent from the consideration of the above equation. It should be noted that in this reaction at least 75 percent of the lead originally employed is not alkylated. Thus, in this reaction, large quantities of lead must be recovered and reprocessed to NaPb alloy in order to make it economical. A further disadvantage of such a large quantity of unreacted lead is that valuable reaction space in the reaction vessel is occuplied by materials which are essentially inert for the manufacture of tetraethyllead under present conditions and mode of operation.

Other processes for the production of organolead compounds, and in particular tetraethyllead, have been devised to consume the lead produced in the above equation. While such processes are satisfactory from the standpoint of lead consumption, they sufier an additional drawback in common with the present commercial process in that they require organo halide as the etbylating agent. One such process is that described in U. S. Patent 2,535,190 wherein lead as, for example that produced in the commercial process, is treated with metallic magnesium and ethyl chloride in the presence of a catalyst, preferably an alkyl ether. Thus, in this process as well as the present commercial process, the tetraethyllead manufacturing operation is restricted by the necessary balance between the metallic sodium required and the organic chlorine in the ethyl chloride.

It is therefore an object of this invention to provide a process for the manufacture of organolead compounds when overcomes the above objections to the present commercial process and those processes which have been proposed more recently as an improvement there over. Particularly, it is an object of the invention to increase the conversion of lead to tetraethyllead above that ob tained in present commercial practice without requiring the use of metallic sodium, metallic lead, or alkyl halogen compounds.

These and other objects of this invention are accomplished by reacting a lead halide with a metallo organic where R is an organic radical and X is a halogen having atomic weight greater than 35, that is chlorine, bromine, and iodine, and M is an alkali metal having an atomic weight greater than 22, that is sodium or potassium. In the preferred embodiment of this process the organic radicals are hydrocarbons and particularly are non-aromatic or aromatic radicals. Among the non-aromatic radicals we can employ alkyl or hydrocarbon substituted alkyl radicals. In general, we prefer the lower alkyl radicals having up to about eight carbon atoms. Among the aromatic radicals which can be employed in the above reaction are included phenyl and hydracarbon substituted phenyl radicals having up to 10 carbon atoms are satisfactory. Thus, the compounds MR may be considered alkylating or arylating agents with respect to the lead in the inorganic lead compound.

Of greatest current importance from a commercial standpoint is the manufacture of tetraethyllead by the process of this invention. This embodiment can be illustrated by reference to the following equation representing the preferred embodiment.

4NaEt+2PbCl,- PbEt,+Pb+4NaCl Illustrative of the alkylating or arylating agents which we can employ are methyl sodium, methyl potassium,

ethyl sodium, ethyl potassium, propyl sodium, propyl potassium, butyl sodium, butyl potassium, amyl sodium, and amyl potassium, and the like up to about octyl sodium and octyl potassium; phenyl sodium, phenyl potassium, benzyl sodium, benzyl potassium, tolyl sodium, tolyl potassium, phenethyl sodium, phenethyl potassium, butylphenyl sodium, diethylphenyl potassium and the like. In addition to the normal alkyl sodium and potassium compounds indicated heretofore, the branch chain isomers can be employed. Likewise, a mixture of two or more compounds MR can be employed along with a redistribution catalyst to produce organolead compounds containing a multiplicity of hydrocarbon radicals. Thus, by employing a mixture of methyl sodium and ethyl sodium and conducting the reaction in the presence of a small quantity of catalyst such as aluminum chloride, the product comprises a mixture of tetramethyllead, trimethyllead, dimethyldiethyllead, methyltriethyllcad, and tetraethyllead in an equilibrium proportion.

Among the preferred lead salts, as shown above, are lead chloride, lead bromide, lead iodide, lead bromo chloride, lead chloride, and lead bromoiodide. Other lead halides can likewise be employed with satisfactory results.

By the process of this invention, as much as 50 percent of the lead in the foregoing lead salts is directly converted to organolead or in particular, in a commercial embodiment, to tetraethyllead. The remaining portion of the lead is in a highly active form as lead metal and is ideally suited for employment in the commercial process employing sodium-lead alloy or in that which proposes the reaction of metallic lead with an alkylating agent in the presence of magnesium and a catalyst. Conversely, the lead so produced by this invention can be recycled eco- .specific reference will be a plug cock 3 nomically to the present process by conversion to the appropriate lead salt.

Our invention is adaptable to the production of organolead compounds generally, such as tetraethyllead. tetramethyllead, dimethyldiethyllead, tetraphenyllead, triethylphenyllead and tetrapropyllead. Nevertheless, for convenience in describing our inventionhereafter, made to tetraethyllead, the most widely known because of its use as an antiknock agent. Whenever, in the following description, this ma terial is referred to, it is to be understood that other organolead compounds or mixtures can be made by our process.

Generally, the process of this invention is conducted as follows. Into a reaction Vessel, preferably a stirred autoclave, is placed the desired quantity of an inert liquid carrier such as, for example, a hydrocarbon of medium boiling range. The lead halide in finely divided solid form is introduced into the autoclave while agitating to create a Suspension thereof in the inert carrier. A suspension of the organo sodium or organo potassium compound in an inert liquid carrier is then fed to the reactor. The autoclave is sealed and moderate heat is applied while continuing the agitation. Contrary to expectation, the two solid phases commence to react as the temperature through a hopper containing is increased. Thereupon, an exothermic reaction ensues and upon reaching the desired reaction temperature, cooling is provided through a jacket in the autoclave. In contrast to other processes for the manufacture of tetraethyllead, when this invention is employed it is not necessary to provide expensive and complex reflux equip ment as, by proper choice of the carrier liquid, the reaction can be conducted in a closed system. Thus, tetraethyllead can be produced without the co-presence of ethyl chloride in the closed vesel. This greatly facilitates control of the reaction and prevents the existence ofan otherwise hazardous operation. After completion of the reaction, the organolead compound produced is in solution in the carrier liquid and the other products, namely the s'odiumor potassium salt and metallic lead can be removed by filtration and the organolead compound removed from the carrier by distillation.

The operation described above can be varied and it is not intended that this invention be limited to the specific sequence of addition of the reactants. For example, the suspension of the organo sodium and potassium compound can be added to the reactor first and then the finely divided lead halide added thereto .with agitation. Other modifications will be evident.

While the above operations were discussed in connection with a batch operation, they can be successfully adapted to a continuous process. In addition to applying the above operation to a continuous process, other modifications of a continuous process can be made, such as first 'mixing together all the reaction materials and then passing them continuously through a suitable reaction zone.

It has been indicated that the process of the present invention is conducted in .the presence of an inert carrier liquid- Hydrocarbons of appropriate boiling point with respect to the organolead compound produced are satisfactory and can be chosen so as to provide a solution of the product suitable for'other applications or so that they can be readily removed by distillation at a temperature at which the organolead compound will not decompose. Other inert carrier liquids are satisfactory and where the product is a liquid such as, for example, in the manufacture of tetraethyllead, the organolead compound itself can be employed as a carrier liquid. In such an operation, economics are effected by obviating the necessity of recovery by other means than merely filtration of the co-produced solids. Another class of carrier liquids comprises the liquid amines and liquid ammonia. The principal criterion of choice there fore, of a carrier, is the physical characteristic of the organolead compound produced, and the inertness of the liquid to the organo sodium or organo potassium reactant. Certain of the aforementioned reactant carriers, while inert to the reactants, exhibit a beneficial effect on the reaction which may be considered catalytic in nature and contribute to the ease of reaction and rapidity of arriving at completion of the reaction at relatively lower temperatures and pressures. n

In general, when conducting this process in the presence of a liquid carrier as above, the amount of-carrier should be proportioned so as to provide adequate heat removal facilities. In general, the load on the heat transfer medium is proportional to the concentration or relative proportion of the reactants and carrier. In a batch operation it is preferred to employ the liquid diluent of organo metallic reactant. In a continuous operation or in a operation providing the maximum heat transfer a more concentrated reactionmixture can be employed wherein as little as equal parts by weight of carrier and organo metallic reactant are employed. In general, it has been found that a more concentrated reaction mixture provides a rapid reaction and, provided adequate heat removal means advantage as the organolead product is subjected to the elevated reaction temperature time thereby minimizing thermal decomposition or undesirable side reactions.

medium,

The sodium and potassium organo compounds em-' arev provided, this is an for the shortest practical ployed in the process ofthis invention can be prepared by methods well action of a sodium with diethyl mercury in the presence of an inert solvent produces sodium ethyl. Cor-.

known in the art. For example, 1'6:-

responding reactions between sodium and potassium and a other organo mercury compounds having the desired organic group are employed for other embodiments of It is not intended, however, that the present invention.

be limited to any particular the scope of this invention method of producing the hydrocarbon carrying reactant.

This invention can be further understood by thefollowing detailed working example of one method of practicing this invention as of tetraethyllead.

. Example I The reactor employed comprises an autoclave with internal agitation, external heating means, and an external means for cooling. Attached to the top thereof sodium suspended in 130 parts of n-hexane andthe autoclave is sealed. The mixture is heated to about C. to initiate the reaction. Since the reaction is ex-: othermic, the heat is then removed and the mixture is directed to the manufacturm cooled to maintain the temperature between about 80' and C. When the temperature drops, as the reaction proceeds, heat is applied to maintain the temperature within the aforementioned range. of 3% hours under these conditions, the agitation is stopped. The mixture is cooled to room temperature and a slight build-up of pressure in the system is re. leased. The reaction mixture is treated with sufficient At the end isopropanol to destroy the excess ethyl sodium. It is 1 then filtered to removesolids. The filtrate is washed with an equal volume of water and the organic layer transferred to a still for the removal, by vacuum distile lation, of the n-hexane and recovery of the tetraethyllead from the mixture,

Similarly, when methyl sodium, propyl sodium, phenyl but a somewhat longer time is required at lower temperatures. In general, a reaction time of between about one-half to twenty hours is employed. In particular, in the manufacture of tetraethyllead with sodium ethyl and lead chloride, we prefer to employe a reaction time of about ten hours or less.

The pressure employed in the reaction vessel is not critical and is usually the autogenous pressure created by the carrier liquid at the temperature employed. Since organolead compounds are relatively toxic, it is desirable to employ a closed vessel in conducting this reaction which may create an elevated pressure if low boiling carrier liquids are employed.

The temperature required to initiate the self-sustaining reaction of this invention varies with the organolead compound being produced. In general, with the lower alkyl lead compounds such as tetraethyllead, it is preferred to employ temperatures in the range of 25 to 150' C. With aryllead compounds, for example tetraphenyllead, it is preferred to operate in the range of 50 to 150 C.

As the reactants in this invention are both solids, and generally a solvent therefore is not employed, it is preferred in order to provide a relatively rapid and controllable reaction to employthe reactants in finely divided form, or at least in the form of small granules.

While it was indicated above that in general a catalyst is not required for the practice of this invention, certain materials do exhibit a catalytic effect upon the reaction and, in many instances, their inclusion in the reaction provides a smoother operation. Typical of such materials are heavy metal iodides as well as iodine itself, organic iodides, certain ketones such as acetone and methyl ethyl ketone, organometallic compounds and ethers and amines as indicated heretofore.

7 Example Ill Amyl sodium is reacted with lead chloride in substantially stoichiometric amounts essentially as described in Example II to produce tetraamyllead in high yield.

The amyl sodium and lead chloride are suspended in a C -C hydrocarbon petroleum fraction as the inert diluent thus permitting operation at atmospheric pressure.

When substituting lead bromide or iodide in the foregoing example, the reaction proceeds satisfactorily at temperatures in the range of 60 to 100 C. or at the atmospheric reflux temperature of a C, to C, hydrocarbon petroleum fraction.

Example IV The procedure of Example II is conducted essentially as described with theexception that phenyl sodium is reacted with lead bromide employing benzene as a diluent. The reaction is conducted for a period of ten hours with the temperature maintained between 110 and 120 C. Tetraphenyllead is obtained in high yield.

Example V When benzyl sodium is reacted with lead bromide in substantially stoichiometric amounts, essentially as described in Example II, tetrabenzyllead is obtained in The following detailed examples serve to illustrate additional specific embodiments of' the present invention. However, the invention is not intended to be limited thereto.

Example I] The equipment employed is the same as that in Example I. The autoclave is flushed with nitrogen then 50 parts of benzene are added thereto, the agitation is commenced and 3.67 parts of lead bromide are dropped from the hopper into the autoclave and the plug cock is closed. A suspension of 1.82 parts of ethyl potassium in 100 parts of benzene is added to this mixture while continuously being agitated. The reactor is then heated to about 80 C. initiating the exothermic reaction. The heat is removed and external cooling is commenced in order to maintain the temperature between 90 and 100 C. The pressure which develops in the system during the reaction is about 20 pounds per square inch gage. At the end of four hours reaction period, the reaction mixture is cooled to room temperature. To the reaction mixture is added sufiicient isopropanol, about 28 parts, in order to destroy excess ethyl potassium. The resulting mixture is filtered to remove the solid constituents. The solids are processed for recovery of the lead value. The filtrate is washed as described in Example I and the organic layer is processed for recovery of the tetraethyllead. Based on the lead converted to organclead, a nearly quantitative yield of tetraethyllead was produced.

In place of the benzene employed in the foregoing high yield. The reaction is conducted for a period of eight hours at a temperature of 110 to 115 C.

The following example will demonstrate another embodiment wherein the tetraethyllead is used as the inert carrier.

.Example VI Ethyl sodium is prepared in the usual manner to result in a suspension comprising 8.30 parts of finely divided ethyl sodium in 260 parts n-hexane. To this suspension is added about 100 parts of tetraethyllead. The mixture is then heated to vaporize essentially all of the hexane therefrom. To the autoclave of Example I is added about 50 parts of tetraethyllead and then 8.4 parts of finely divided lead chloride are added thereto with agitation. The suspension of the ethyl sodium in tetraethyllead is added to the autoclave and it is sealed. The autoclave is heated to about C. and then by means of cooling and heating, as necessary, the reaction temperature is maintained between 80 and C. At the end of seven hours the reaction mixture is cooled to room temperature, treated with alcohol, washed and filtered as in the above examples. The tetraethyllead prepared in this manner is recovered in high yield and high purity.

A particularly advantageous and preferred method of utilizing the process of this invention as specifically directed to a commercial method of manufacturing tetraethyllead comprises starting with free, sodium and hydriding to produce the corresponding sodium hydride as the first stage. A second stage then comprises reacting said hydride with ethylene preferably in the presence of a liquid diluent suitable as a carrier for the ethyl sodium which is thereafter reacted with the lead chloride in accordance with the foregoing description of the present invention.

We claim:

1. A process for making hydrocarbon lead compounds which comprises reacting a hydrocarbon metal compound of a metal selected from the group consisting of sodium from the group consisting of alkyl and aryl radicals with a lead halide of a halogen selected from the group consisting of chloride, bromine and iodine.,

2. The processof claim 1 wherein the reaction is conducted in the presence 0 an inert liquid carrier.

3. The process of claim 2 wherein the reaction is com ducted at a temperature between about 25 to 150 C.

4. A process for making alkyllead compounds which comprises reacting a lead halide of a halogen selected from the group consisting of chlorine, bromine and iodine with an alkyl sodium compound wherein the alkyl radical contains up to about 8 carbon atoms. 7

5. The process for manufacture of tetraethyllead which Y comprises reacting sodium ethyl with lead chloride.

6. The process of claim 5 wherein the reaction is con-' ducted in the presence of a liquid hydrocarbon at a tem- 5 perature between about 25 to 150 C.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Sidgwick: Chemical Elements and Their Compounds,

vol. I, p. 71, Oxford Press Great Britain (1950), citing Gilman et 31.: I. A. C. S., 54, 1265 (1932).

I. A. C. S. 54 (1932), p. 3726. I

Ziegler et a1. Mar. 26, 1957 1 

1. A PROCESS FOR MAKING HYDROCARBON LEAD COMPOUNDS WHICH COMPRISES REACTING A HYDROCARBON METAL COMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM WHEREIN THE HYDROCARBON RADICAL CONTAINS UP TO ABOUT 10 CARBON ATOMS INCLUSIVE AND IS SELECTED FROM THE GROUP CONSISTING OF ALKYL AND ARYL RADICALS WITH A LEAD HALIDE OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORIDE, BROMINE AND IODINE. 